Nitrosodisulphonic Acid, NO(SO3H)2

Nitrosodisulphonic Acid, Peroxylaminic Acid, or Sulphazilic Acid, NO(SO3H)2 is only known in solution; it may be obtained by the passage of equal volumes of nitric oxide and air into a cooled saturated solution of sulphur dioxide in sulphuric acid. It forms an intense bluish-violet solution:

2NO + O + 2SO2 + H2O = 2[NO(SO3H)], 2[NO(SO3H)] = NO + NO(SO3H)2.

It is also formed by passing sulphur dioxide into a solution of sodium nitrite in sulphuric acid:

2NO2(SO3H) + 3SO2 + 2H2O = 2NO(SO3H)2 + H2SO4.

Nitrosodisulphonic acid decomposes spontaneously into sulphuric acid, sulphur dioxide and nitric oxide. Its solution is rapidly decolorised on shaking with air or on mixing with hydrogen peroxide, per- mono- or perdi-sulphuric acid, nitric acid, chlorine or potassium chlorate. Most metallic oxides and carbonates decompose the solution, being converted into sulphates.